Chapter 10 - Work, energy and power Flashcards
Give examples of energy stores
- gravitational potential stores (position of objects in gravitational field)
- thermal stores (hot objects)
- elastic stores ( objects compressed or stretched)
Give ways energy can be transferred between objects
- Radiation (e.g. light)
- electrically
- mechanically
Define the principle of conservation of energy
Energy cannot be created or destroyed only converted to other forms
What is the equation for work done?
work done = force x distance moved in direction of force
What is the definition of work done?
Energy transferred by a force in the direction of the force
or
Energy transferred by the component of the force in the direction the object is moving.
How do you find work done if the force is not acting in the direction of motion?
Find component of force in direction of motion (= F x cos angle)
Work done = Fs cos angle
What does the area under force distance graph show?
Work done
How do you find out the work done to stretch a spring?
Draw a graph of force against extension
area = work done
work done = 1/2 x F x change in length
What is kinetic energy? Give the equation
Energy of an object due to its motion
Ek = 1/2 x m x v^2
What is gravitational potential energy? Give the equation
Energy of an object due to its position
Ep = mgh
Describe the changes of a falling ball
Potential energy transferred to kinetic energy as it increases in speed (as it falls).
gain of Kinetic energy = loss of gravitational potential energy
Define power
Rate of energy transfer
Give the equation for power
Power (W) = energy transferred (J)/time(s)
What is the power equation linking power, force and velocity?
Power (W) = force (N) x velocity (ms^-1)
What is the equation for efficiency?
efficiency = useful energy transferred / energy supplied
or
efficiency = useful output power / input power
